3 files changed, 137 insertions, 6 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 2355bddad8de..2bac4ba1d1d3 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -549,6 +549,136 @@ repeat:
 }
 
 /*
+ * destroy a single subtree of dentries for unmount
+ * - see the comments on shrink_dcache_for_umount() for a description of the
+ *   locking
+ */
+static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
+{
+        struct dentry *parent;
+
+        BUG_ON(!IS_ROOT(dentry));
+
+        /* detach this root from the system */
+        spin_lock(&dcache_lock);
+        if (!list_empty(&dentry->d_lru)) {
+                dentry_stat.nr_unused--;
+                list_del_init(&dentry->d_lru);
+        }
+        __d_drop(dentry);
+        spin_unlock(&dcache_lock);
+
+        for (;;) {
+                /* descend to the first leaf in the current subtree */
+                while (!list_empty(&dentry->d_subdirs)) {
+                        struct dentry *loop;
+
+                        /* this is a branch with children - detach all of them
+                         * from the system in one go */
+                        spin_lock(&dcache_lock);
+                        list_for_each_entry(loop, &dentry->d_subdirs,
+                                            d_u.d_child) {
+                                if (!list_empty(&loop->d_lru)) {
+                                        dentry_stat.nr_unused--;
+                                        list_del_init(&loop->d_lru);
+                                }
+
+                                __d_drop(loop);
+                                cond_resched_lock(&dcache_lock);
+                        }
+                        spin_unlock(&dcache_lock);
+
+                        /* move to the first child */
+                        dentry = list_entry(dentry->d_subdirs.next,
+                                            struct dentry, d_u.d_child);
+                }
+
+                /* consume the dentries from this leaf up through its parents
+                 * until we find one with children or run out altogether */
+                do {
+                        struct inode *inode;
+
+                        if (atomic_read(&dentry->d_count) != 0) {
+                                printk(KERN_ERR
+                                       "BUG: Dentry %p{i=%lx,n=%s}"
+                                       " still in use (%d)"
+                                       " [unmount of %s %s]\n",
+                                       dentry,
+                                       dentry->d_inode ?
+                                       dentry->d_inode->i_ino : 0UL,
+                                       dentry->d_name.name,
+                                       atomic_read(&dentry->d_count),
+                                       dentry->d_sb->s_type->name,
+                                       dentry->d_sb->s_id);
+                                BUG();
+                        }
+
+                        parent = dentry->d_parent;
+                        if (parent == dentry)
+                                parent = NULL;
+                        else
+                                atomic_dec(&parent->d_count);
+
+                        list_del(&dentry->d_u.d_child);
+                        dentry_stat.nr_dentry--;        /* For d_free, below */
+
+                        inode = dentry->d_inode;
+                        if (inode) {
+                                dentry->d_inode = NULL;
+                                list_del_init(&dentry->d_alias);
+                                if (dentry->d_op && dentry->d_op->d_iput)
+                                        dentry->d_op->d_iput(dentry, inode);
+                                else
+                                        iput(inode);
+                        }
+
+                        d_free(dentry);
+
+                        /* finished when we fall off the top of the tree,
+                         * otherwise we ascend to the parent and move to the
+                         * next sibling if there is one */
+                        if (!parent)
+                                return;
+
+                        dentry = parent;
+
+                } while (list_empty(&dentry->d_subdirs));
+
+                dentry = list_entry(dentry->d_subdirs.next,
+                                    struct dentry, d_u.d_child);
+        }
+}
+
+/*
+ * destroy the dentries attached to a superblock on unmounting
+ * - we don't need to use dentry->d_lock, and only need dcache_lock when
+ *   removing the dentry from the system lists and hashes because:
+ *   - the superblock is detached from all mountings and open files, so the
+ *     dentry trees will not be rearranged by the VFS
+ *   - s_umount is write-locked, so the memory pressure shrinker will ignore
+ *     any dentries belonging to this superblock that it comes across
+ *   - the filesystem itself is no longer permitted to rearrange the dentries
+ *     in this superblock
+ */
+void shrink_dcache_for_umount(struct super_block *sb)
+{
+        struct dentry *dentry;
+
+        if (down_read_trylock(&sb->s_umount))
+                BUG();
+
+        dentry = sb->s_root;
+        sb->s_root = NULL;
+        atomic_dec(&dentry->d_count);
+        shrink_dcache_for_umount_subtree(dentry);
+
+        while (!hlist_empty(&sb->s_anon)) {
+                dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
+                shrink_dcache_for_umount_subtree(dentry);
+        }
+}
+
+/*
  * Search for at least 1 mount point in the dentry's subdirs.
  * We descend to the next level whenever the d_subdirs
  * list is non-empty and continue searching.
diff --git a/fs/super.c b/fs/super.c
index aec99ddbe53f..47e554c12e76 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -260,17 +260,17 @@ int fsync_super(struct super_block *sb)
  *      that need destruction out of superblock, call generic_shutdown_super()
  *      and release aforementioned objects.  Note: dentries and inodes _are_
  *      taken care of and do not need specific handling.
+ *
+ *      Upon calling this function, the filesystem may no longer alter or
+ *      rearrange the set of dentries belonging to this super_block, nor may it
+ *      change the attachments of dentries to inodes.
  */
 void generic_shutdown_super(struct super_block *sb)
 {
-        struct dentry *root = sb->s_root;
         struct super_operations *sop = sb->s_op;
 
-        if (root) {
-                sb->s_root = NULL;
-                shrink_dcache_parent(root);
-                shrink_dcache_sb(sb);
-                dput(root);
+        if (sb->s_root) {
+                shrink_dcache_for_umount(sb);
                 fsync_super(sb);
                 lock_super(sb);
                 sb->s_flags &= ~MS_ACTIVE;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 44605be59409..63f64a9a5bf7 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -230,6 +230,7 @@ extern struct dentry * d_alloc_anon(struct inode *);
 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
 extern void shrink_dcache_sb(struct super_block *);
 extern void shrink_dcache_parent(struct dentry *);
+extern void shrink_dcache_for_umount(struct super_block *);
 extern int d_invalidate(struct dentry *);
 
 /* only used at mount-time */